In a large bowl, mix flour, sugar, and salt. Cut in cold butter using a pastry cutter or fingers until mixture resembles coarse crumbs.

1. Add ice water, one tablespoon at a time, mixing until dough comes together. Divide in half, flatten into disks, wrap in plastic, and chill for at least 30 minutes.
2. While dough chills, prepare the filling: cook diced apples with brown sugar, cinnamon, nutmeg, and cornstarch in a saucepan over medium heat until softened and thickened. Let cool completely.
3. Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
4. Roll out chilled dough on a floured surface to about 1/8-inch thickness. Cut into 4- to 5-inch circles or squares.
5. Spoon a tablespoon or so of apple filling onto the center of each piece. Fold dough over to form a half-moon or rectangle. Press edges with a fork to seal and cut a small vent on top.
6. Brush each pie with egg wash and sprinkle with coarse sugar, if desired.
7. Bake for 20–25 minutes, or until golden brown and flaky.
8. Let cool slightly before serving. Drizzle with glaze if using.